Search

A massive toppling failure occurred at the edge of the Furnas Reservoir at 12:30 (UTC-03) on 8 January 2022, in Brazil. The toppling belongs to single-block toppling with a volume of about 3.32 × 102 m3 and caused 10 deaths and 32 injuries. Field investigation, numerical analysis, and base friction tests were performed to explore the failure characteristics and mechanism of the toppling. A conceptual model of the toppling mechanism was constructed and the toppling process was divided into four stages: foundation erosion and weakening stage, crack propagation and dislocation stage, opening up and rotation stage, and disintegration and collapse stage. A series of real three-dimensional numerical simulations was performed to clarify the toppling evolution and related triggering mechanism using the finite difference program FLAC3D. Two different alternatives of triggering mechanism for the toppling were comparatively analyzed, the first with a reduction in the shear strength of the weak foundation layer believed to represent the foundation weakening mechanism, and the second with removal of the weak layer believed to represent the foundation erosion mechanism. We found that the foundation weakening of the weak layer resulted in a sliding mechanism of the block, while the foundation erosion resulted in a clear toppling mechanism of the block. The base friction test was conducted to investigate the toppling process and to verify the numerical results over a limited time span. The experimental evidence demonstrated a good agreement with the numerical results as well as those observations in the field. We concluded that the slope was in a critical state due to the foundation erosion of the weak layer, while the heavy rainfall triggered the toppling. It is emphasized that the undermining of the slope foundation and/or existed cavities induced by the foundation erosion played a vital role in the formation of the toppling. Moreover, a produced vertical crack or the propagation of an existed crack in the rear part of the slope may be signs of movements and thought of precursors of the single-block toppling. Dealing with the eroded cavities was suggested to be an effective way to prevent the toppling in the Furnas Reservoir, such as backfilling the eroded cavities with masonry rubble and/or grouting. The understanding of the toppling characteristics and mechanism may offer a reference for single-block toppling issues, such as its movement characteristics and failure mechanism, and may be used for stability analysis and disaster identification of potential failures. [ABSTRACT FROM AUTHOR]

A large-scale landslide occurred at the waste dump of Dagushan open-pit iron mine in Anshan, China. The landslide caused the collapse of 8.45 × 106 m3 of waste rock with a maximum runout distance of 150 m, resulting in the burial of 7.2 × 104 m2 of the site and destruction of numerous buildings and roads. Based on field investigations, laboratory tests, and numerical simulations, the failure characteristics of the landslide were investigated and the inducing factors as well as the failure mechanism were analyzed. According to field surveys, the landslide area was divided into the traction failure area, the main sliding area, and the accumulation area. A series of in situ and laboratory tests were performed to obtain the engineering properties of the waste material and the foundation silty clay of the waste dump. Then, a conceptual model of the landslide mechanism was constructed and the failure process was divided into four stages: foundation weakening stage, shearing and dislocation stage, sliding and shearing out stage, and tractive sliding stage. Two- and three-dimensional numerical simulations were performed to clarify the landslide evolution and related triggering mechanism combining the strength reduction method with the finite difference program FLAC3D. The results show that the saturation and weakening of foundation silty clay under the action of groundwater were the trigger factors of the landslide, which resulted in the shear failure of the weak foundation, and further triggered the mass collapse and formed the large-scale landslide. The sliding surface passed through the overlying waste materials and progressed along the weak foundation of the slope. The failure pattern obtained by numerical simulations matched closely with the observations in the field. The understanding of the landslide characteristics and mechanism may offer a reference for disaster identification and stability analysis of large-scale waste dumps around the world. [ABSTRACT FROM AUTHOR]

A rainfall-induced landslide occurred in the north highwall of the Fushun west open pit at 5:00 (UTC + 8) on July 26, 2016, in China. The landslide was about 3.1 × 106 m3 and caused considerable destruction of houses, roads, and railways. Field investigations, laboratory tests, and numerical analyses have been performed to explore the failure characteristics and formation mechanism of the landslide. The landslide was divided into three parts: the crack area, the sliding body area, and the accumulation area. The X-ray diffraction and scanning electron microscope techniques were used to reveal the mineral composition and microstructure of the landslide material. Then, a conceptual model of the landslide mechanism was constructed and the process of the landslide was divided into four stages: unloading and cracking stage; sliding and partial locking stage; shearing out and failure stage; and flowing and accumulating stage. A combined seepage and stability analysis was performed to explore the mechanism of the landslide by numerical simulation. The relationship of volumetric water content and hydraulic conductivity to matric suction was established to describe the hydraulic characteristics of the slope material under infiltration. The results show that the maximum matric suction in the slope decreases continually with the increase of rainfall intensity and duration, and the north highwall will not be stable after 7.2 h for 16 mm/h of rainfall. The original slope was stable and heavy rainfall triggered the landslide, and the obtained critical failure surface matched the field survey closely. The findings improved understanding of the failure mechanism and process of rainfall-induced landslides may be used for evaluating the stability of slopes and early identification for both active and inactive open-pit mines. [ABSTRACT FROM AUTHOR]

A landslide occurred on November 24, 2019, in weathered phyllite at the western longwall of Yabaling open pit of Anqian iron mine in Anshan City, Liaoning Province, China. The landslide was estimated to be 3.0 × 104 m3 in volume and caused severe damage to the road of transporting waste materials. This landslide was a typical jointed rock mass landslide, and the cause of the landslide was related to four factors: open-pit mining activity, the weak rock, discontinuities, and the high rainfall. According to the failure characteristics, the landslide area was divided into three parts: the tension-cracking area, the sliding-deformation area, and the colluvium area. The failure mechanism of the landslide was investigated through a back analysis combining nonlinear Hoek–Brown criterion and FLAC3D program with a parameter reduction technique. The results showed that the predicted sliding surface at the critical state matched closely the field observations. A remedial scheme of landslide stabilization including four rows of micropiles was proposed and the stabilization mechanism of the micropiles was discussed. The shear strain increment contours show that the micropiles arrested the original sliding surface and controlled the movement of the sliding mass behind them, and thereby significantly improved the stability of the landslide. This paper also presents the results obtained from the parametric analysis in order to understand the impact of strength parameters on the long-term stability of the stabilized slope. The findings improved understanding of the failure characteristics and mechanism of jointed rock mass landslides may be used for evaluating the stability of slopes and early identification for both active and inactive open-pit mines. [ABSTRACT FROM AUTHOR]

Owing to the heavy rainfall, a landslide occurred at the Anqian Iron mine, at 18:00(UTC + 8) on November 24, 2019, in China. The landslide was about 3.0 × 104 m3 and caused damage to the road of transporting waste materials. Failure characteristics and the mechanism of this landslide were analyzed in this study. The landslide area was divided into three parts: the rear tension cracking area, the middle sliding deformation area, and the front colluvium area. A contact-free measuring technique using the new ShapeMetrix3D system was applied and 204 joints were analyzed based on equal-angle stereographic projection. Thus, a conceptual model of the mechanism of the landslide was constructed and the formation process of the landslide was divided into three stages: the first shearing and dislocation stage; the second sliding, front bulging, and rear tractive cracking stage; and the third local rock mass collapse and colluvium depositing stage. Numerical modeling was performed to discover the landslide mechanism by progressively reducing the shear strength of rock mass. The results showed that the original slope was stable, whereas heavy rainfall triggered the landslide, and the predicted failure surface matched closely the field investigations. The factor of safety obtained by real three-dimensional analyses was slightly higher than that obtained by plane problem analyses, and the difference was attributed to the three-dimensional effect of the landslide. This paper also presents the results obtained from the parametric analysis in order to understand the impact of shear strength parameters on the overall stability of the slope. [ABSTRACT FROM AUTHOR]